Hydraulic apparatus



Nov. 22, 1949 c. E. ADAMS E AL HYDRAULIQ APPARATUS 2 Sheets-Sheet .1

I I INVENZ 'ORJ Ce c131 E.Adorns I Ellis I-LBorn 57 @M 5% Filed March 8,1946 Nov. 22, 1949 c. ADAMS ET AL 2,489,069

HYDRAULIC APPARATUS Filed March 8, l9 46 2 Sheets-Sheet 2 V INVENTORSCecil EAdums Ellis HJBorn Patented Nov. 22, 1949 HYDRAULIC APPARATUSCecil E. Adams and Ellis H. Born, Columbus, Ohio, assignors to IheDenison Engineering Company, Columbus, Ohio Application March 8, 1946,Serial No. 652,937

Claims.

This invention relates to hydraulic apparatus and is particularlydirected to apparatus for forming articles or objects by hydraulicpressure.

An object of this invention is to provide a, hy-

draulic press having a forming ram and a second ram operable inconjunction with the forming ram to knock out or eject the formed piecesfrom dies or similar tools used with the forming ram.

Another object of the invention is to provide a press having a hydraulicram operating unit, a hydraulically operated unit for a knock out ramand a hydraulic circuit for controlling the operation of the units tosecure a particular sequence of operations of the rams.

A further object is to provide a ram-operating unit of particularconstruction which will function, when the ram is moved in a certaindirection, to supply auxiliary operating fluid to another unit, theconstruction being such that when the latter unit no longer needs theauxiliary operating fluid, the supply will be discontinued.

A still further object is to so construct the ram operating unit,mentioned in the preceding paragraph, and arrange the hydraulic circuitincorporating the unit and a knock out cylinder, or other power unit,that when the former reaches a certain stage of operation the latterwill move or return to a predetermined position or stage of operation.

Another object is to provide the hydraulic system incorporating thevarious ram operating units with a valve for the selective operation ofcertain of the ram operating units in a predetermined manner.

An object of the invention also is to provide a press having apressing-ram operating unit including piston cylinders of differentsizes and pistons disposed in the cylinders and connected for movementin unison, the total of the areas of the pistons being effective whenmoving in one direction, the area of one piston being effective when thepistons are moving in the opposite direction to transmit at least partof the fluid used in the pressing operation, to an ejecting device, thedifierence in areas of the pistons providing for a differential in therate of travel of or the distance traveled by the pressing ram on itsreturn stroke and the distance moved by the ejecting device.

Another object is to provide a hydraulic circuit for a pressingmechanism of the type having a pressing ram and a knock out ram, whichmay cause the knock out ram to move at a different rate of speed whenthe pressing ram has reached a predetermined point in its travel, thecircuit being provided with mechanism to permit the selective return ofthe knock out ram to inactive position either manually or otherwise.

It is an object of this invention to provide hydraulic pressingmechanism having a, pressing ram and an ejecting ram and a hydrauliccircuit for operating the rams, which circuit will provide a pluralityof modes of operation, such, for example, as the agitation of thematerial being i pressed during the pressing operation; the subjectionof the formed article to pressure between the rams. during the ejectionthereof; the subjection of the formed article to pressure between therams during a part only of the ejection stroke,

theejection of the formed article while being held between the ramswithout the exertion of pressure thereon, and the ejection of the formedarticle with the pressing ram separated therefrom.

An object of the invention also is to provide a v pressing mechanismhaving pressing and ejecting rams arranged in a hydraulic circuit ofsuch type that the rams respond in unison to the operationalcharacteristics of the control mechanism therea for, in other words, thecontrol may be actuated to cause the pressing ram to be advanced intoforming contact with the material; then, the control ma be manipulatedrapidly between pressing and return positions to cause the ram toreciprocate through a portion of its travel and the ejecting ram willmove in a similar manner, the placing of the control in return positioncausing the return stroke of the pressing ram which in turn causes theejection stroke of the ejecting ram.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred form of embodiment of the invention isclearly shown.

In the drawings:

Fig. 1 is a diagrammatic view of a hydraulic circuit for a pressingmechanism constructed in accordance with the present invention. 7

Fig. 2 is a diagrammatic view of a slightly modified circuit.

Referring more particularly to Fig. 1 of the drawings, the numeralllldesignates generally a fluid pressure source which includes, a,reservoir H, a motor driven pump l2, a pressure relief valve l3 andfluid lines l4, l5 and I6 leading to and from the pump and from thevalve [3 to the reservoir, respectively. Fluid line l5 has a branch I!extending therefrom to a control valve mechanism is employed to governthe flow of fluid under pressure from the source ID to -a primary pgwerunit designated generally by the numeral 2 The unit 20 includes a fluidcylinder 2| having a pair of sections 22 and 23 of different diameters.These cylinder sections 22 and 23 receive a piston unit with beads 24and 25 disposed for movement in the sections 22 and 23, respectively,and connected by stem 25 to form a unit. Ram 21 projects from the piston24 through the end wall of the cylinder to perform useful work. Fluidlines 28 and 32:. extend from the control valve mechanism i8, which. inthe present illustration is of the conventional four-way type but forspecial operations may be of other types such as those illustrated inthe copending applications of Cecil E. Adams, Serial Nos. 545,700 nowPatent No. 2,464,283; 545,701, now Patent No.. 2,21 589,163; 594,963. tothe cylindersections- 2.2 at-ope. posite ends of piston 24. Through themanipulation of the spool 31 of the valve [8,, fluid under pressure fromthe source may be alternately applied to opposite ends of piston 24 .toefiect reciprocation of the piston and the ram 21. The above mentionedcopending applications illustrate the manner in which the control valvemay be automatically or manually manipulated to -secure thereciprocation oi the. ram through either the. full stroke or part ofsuch stroke.

To utilize the. pressing force ofthe ram 21, a

mold. 32 having av cavity 33 is supported in registration with the ram21, the latter may be pro-. vided with a suitable tool for cooperationwiththe mold .32 depending upon the shape of the article being pressed.In the present illustration, no additional tool is employed, the lowerend of the ram entering the cavity 33. to form a slug 0r v I Accordingto. the invention, the lower end of the. cavity 33 is closed by a secondram 35 which projects. outwardly from a piston as forming a part of asecondary power unit .31. This unit has a cylinder 38. and is arrangedon the opposite side oi the moldslfrom the primary power unit,

the ram 35, in addition to forming the bottom wall of the cavity,serving .as. an ejector or knock out plunger for the finished article34. The piston .32 and, ram 35 are normally urged toward a retractedposition by a..spring All-surrounding the ram .35. between the piston 36and the inner end of the cylinder 38-and when fully retracted, the outerend of the ram 35. will be properly positioned in the mold 32 for theformation of an article. This position may bevaried to change thecapacity-of thecavity 33 through the adjustment of a stop means, such asthe. screw 39, dise posed at the lower end of the unit for engagement bya balancing stem. projecting from the. piston .35 on the side oppositethe ram 35.

In the operationoi the pressing mechanism, the mold cavity 33 is chargedwith the material to be pressed and the spool 3| moved upwardly, by.suitable means such as the foot lever 42 and shipperrod .23, todirectfluid from line l1 to line.

25 and the upper end of cylinder section 22. A portion of this fluidalso flows from line. :28 through a branch line 44, past check valve 45and through line 26. tothe enter and of cylinder section 23. The .forceof this fluid acts upon the end of. piston head 25. and operates inconjunction with the .fluid supplied to the upper end of cylindersection22 tomove the pistonand ram assembly in the power or working stroke. Asthe ram moves into the moldlcavity, the material therein is compressedto form the desired article. After the maximum pressure -for which therelief valve I3 has been set, has been exerted by the ram 21,- the lever42 is manipulated to move spool 35 into position to direct fluid fromline 11 through line 33 to the lower end of cylinder section 22 toefiect the elevation or retraction of ram 2?. In the formation ofarticles from some materials it may be desirable to impart a series ofpressure impulses to the article being formed. This may be accomplishedby oscillating the spool 3i between elevated and lowered positions afterthe initial pressing stroke of-the ram has been completed. When thepressing mechanism is provided with control means of the type shown inthe above mentioned copending Adams applications, this series'ofimpulses, consisting of short reciprocations of the ram, may be eithermanually or automatically secured. As is customary in presses of thischaracter, the fluid exhausted from cylinder 22 during the workingstroke is returned tov the fluid reservoir through an exhaust line 41.On the return movement of the ram at least a portion of the exhaustfluid is utilized to effect the operation of the secondary power unit inthe ejection stroke of the plunger 35. This feature is, accomplished byextending a branch line from the line 45 to the outer end ofthesecondary cylinder 38. Thus when fluid is exhausted from cylindersection 23 it will flow through lines- 4t and is to the outer end-ofcylinder-:38 causing piser 35. and piston 36 are retracted or returnedtotheir initial positions during each pressing stroke of the ram 21, thefluid beneath piston 36 being forced through lines 48 and 4.6 to theouter end of cylinder section 23. It will be obvious from the foregoingthat when a series of impulses are imparted to an article, the ejectionplunger ime parts a thrust to the article during each; upward movementof the pressing ram. In this manner, the material is agitated duringthe; forming op-. eration.

Since it is desirable in some instances, to have the pressing ram 21move away from or separate from the formed article beiore the latter isejected, only a portion of the fluid exhausted during the retraction ofthe ram in such in stances, is employed .to move theejection plunger.The efiective area of the piston used to operate this plunger is alsocalculated so that the fluid supplied to the cylinder 38 will cause theplunger 35 to move at a slower rate than the'ram 21. The check valve 25between lines 46 and 44 prevents the fluid being exhausted from theouter end of cylinder section 23 from flowing to the exhaust line 31. Itis essential, however, to permit this exhaust fluid to reach the exhaustline ll' after the piston 25 has completed its necessary stroke. Aby-pass line 50 is, therefore, extended between lines it and 44 aroundthe check valve 45. This by-pass line is provided with a pressure reliefvalve 55 which is adjusted to the maximum pressure necessary for theoperation of the ejection.

plunger 35.

. When fully automatic operation is desired it is necessary to returnthe plunger 35 to a retracted position after the formed article 34 hasbeen removed to permit a new charge of material to be inserted in themold. This auto-. matic retraction of the ejector plunger is ssenceformed withv a socket .52. forv the slidable reception of a valve plug5.3. A spring 54-disposed be tween the plug 53' and the inner end of thesock et 52 normally urges the. plug to a. position to preventcommunication between passages 55 and the socket 52, the passagesextendingtothe inner'end of the head25.. The cylinder section 23 has anadjustable stop screw 56 projecting there-- into from the outer end;This screw is disposed to engage the plug 53 as the ram 2! and pistonthereof are retracted and cause relative move-j ment between the plug 53and the piston 25 whereby communication. between opposite ends ofthepiston head 25 will be established. When the passages and the socket 52are in communication, the spring 4'8 may expand and force the piston 36toward the outer end of the cylinder 38. Fluid beneath the piston 36.will be exhausted through-lines 48 and 46 to the outer end of cylinder23;. Since communication is established between opposite ends of piston25 this fluid will flow through lines 28, 44 and 51 to the inner end ofcylinder 38. g

Pressure and suction created by the recipro. cation of the plug 53 arerelieved by a small oriflce 58' extending through the plug andillustrated in Fig. 1 'bydotted lines.

In some instances it may be desirable to se:- lectively return theplunger 35 to a retracted position. For instance, it may be advantageousto retain the ejecting ram in an extended condition to support theformed article 34 until it may be manually removed. In such operation,the pressing ram and its piston structure may be fully retracted beforethe removal of the article. To prevent the automatic retraction of theejecting plunger in the manner pointed out above, the stop screw 56 isadjusted until the plug 53 cannot-engage it during the retraction of thepressing ram. After the formed article 34 is removed, the plunger 35 maybe retracted through'the operation of a normally closed valve 59arranged in a by-pass line 6-0 extending between fiuid lines 48 and 51.If the valve 59 is opened'when the-plunger 35 is extended, fluid mayflow through line 68 from one end of cylinder 38 to theother permittingspring so to move piston 36 and plunger 35 to normal, retractedpositions. It' should be obvious that valve 59 could be-operated eithermanually or mechani-' v cally depending upon the nature of the workbeing performed.

The invention is susceptible to considerable modification. For example,Fig. 2 shows a by draulic circuit 65' of modified form for use on apressing mechanism. As in the first form of the invention, the circuit65 includes a fluid pressure source 86 similar to that shown at I 8 inFig. 1. The pressure line 51 extending from the source 66 is connectedto a control valve 68 which may also be of the conventional four-way orany other reversing type four-way valve. Cylinder lines: and H lead-fromthe valve 58 to the ends ofa power cylinder 12. Line 10 has a springpressed" check'valve 13 incorporated therein for a purpose to be' laterdescribed. Cylinder; l2 slidably' receivesa iston 14 from one-end ofwhich proa jects a ram this ram serves to do useful work and correspondsto ram 21 in the mechanism shown in Fig. 1".

- I The circuitof Fig. 2 also includes an ejection.

or knock-out plunger 16 corresponding to that indicated by in Fig. 1.Plunger; 16 forms. a part of a piston 11 disposed for reciprocation; in.cylinder 18.- A coil spring surrounding plunger.

1.6 and engaging piston 71 resiliently urges the plunger toward aretracted: position. This later position is determined by a stop screw80 ad.- justably. receivedby the outer end of the cylinder 18.

V In Fig. 2, the circuitincludes a pressure operated valve sl having aspool 82 disposed for sliding. movement in a cylinder 83. Fluid lines84and8'5 extend to opposite ends of this cylinder, line-84 branchingfrom line 10 and line- 85 leading from the outer end of the cylinder 12.When. fluid. is. directed from. the pressure source .66. to the outerend of the cylinder 12 bythe valve 68, the springpressed check valvewill resist now through the line 18 causing a slight increase inpressure in line 10 which will be transmitted by line to the end ofcylinder 83 and applied tothe endof spool 82 to move the same to aposition to pre'ventoommunication between line 85' and'a line .86leading from valve 8| to the lower or outer endofcylinder'lB.

After'ram '15 has completed a pressing stroke, valve 68 is operated todirect fluid from the pressure source to thelower or inner end ofcylinder. l2'to effect the retraction ofthe ram.75. When ram 15 somoves, fluid exhaustedfrom the outer end of cylinder l2will-be'prevented from flowing to va1ve'68 through line Why the checkvalve 13. Such exhaust fluid must, therefore, flow through line 85 tocylinder as where its force will be applied to' the end of spool 82 tomove it to a valve opening position.v The fluid may then flowthrough-line 86 to the outer end of cylinder 18. Line 86 contains apressure relief val-ve 8'! and a normally open spool valve 88 which isarranged to be operated by a cam 98,

v fixed for movement, in this instance, with ram 15. It should beobvious that cam 98 could be moved either by-handor by some othermechanismif desired.

When ram 75 is being retracted and a valve 88 is open-allthe'fluid beingexhausted from cylinder 12 may fiow'tocylinder 18. This fluid will tendto cause theram 16 to move at a greater rate than ram 75. In'theformation ofsomeproducts this tendency is desirable because it isadvantageous to exert a squeezing action on the product'as it is beingejected. The force exerted by the ram 16 is determinedby thesetting' ofthe relief valve 81' which also serves to relieve. excessive pressure iff ram 16 should be stopped'before reaching the end of its travel orwhenthis'ram reaches the limit of its I movement retracted.

Some products require the relative positions of the rams T5 and 16 to bemaintained throughout a now control mechanism 9d of conventional'comstruction arranged in a by-pass line fizextending. around valve 88: Torenderthe mechanism 91.

eifeotive; valve 88" must be closed by cam. 58 or.

otherwise at some Point during the retraction oi;

ram 15 If the ram 15 be required to separate.

from the article during ejection, the mechanism' 9| is adjusted to causeplungerv it to. move at a slower rate than ram [5, the. excess ofexhaust fluid necessary. to operate'plun'ger 15 being. re.- turnedtozthe reservoir. by relief valve 87..

Retraction ofjplunger 'lGjis effected by opening a. normallyclosed-valve 93 connected in a fluid line 9'4jdisposed betweenline .86and another liner95 15 connecting the upner. -or inner endof cylinder'1.8.-

before ram is completely 'aaaooc of the invention first described, valve68 may bemanually operated, or-valve means of the type shown in theabove mentioned copending applications may be provided which willautomatically operate, to impart a series of sharp pressing impacts tothe article being formed. During this series of impacts, the pressingram is repeatedly advanced and retracted and similar movement of theejecting plunger also occurs, the latter being retracted as the formeradvances. To permit this retraction of the ejecting plunger or ram it isnecessary to provide an outlet for the fluid in the outer end ofcylinder 18. Such an outlet is secured in the circuit shown in Fig. 2,by extending a fluid line 9'! from the cylinder 83, between the lands onthe spool 82, to the reservoir of the pressure source 66. Thus whenfluid pressure is from said first power unit during retraction of saidfirst ram to said second power unit to cause the projection of thesecond ram; means for limiting the projecting movement of said secondram; relief valve means in said fluid conducting means to limit thepressure in said fluid conducting means after the motion of saidsecondjram has been limited; means normally urging said second ramtoward a retracted position; and valve means operatedby the piston ofthe first power unit at a predetermined point during the retraction ofthe first ram to discontinue the direction of exhaust fluid to saidsecond power unit and direct it to exhaust, said valve means alsoserving at the same time to establish communication between the oppositeends ofsaid second power unit.

3. In a hydraulic pressing apparatus, a source of fluid pressure; firstand second power units having reciprocable rams; a control valvemechanism between said source of pressure and the supplied to line 18 tocause the advance of ram l spool 82 will be moved to a position tointerrupt communication between lines 85 and 86 and establish aconnection between the latter and line 91 whereby fluid exhausted fromthe outer end of cylinder 18 may flow without obstruction to thereservoir. 7

The circuits shown and described, as well as others falling within thescope of the appended claims are particularly suited for use inpelleting or similar operations wherein material is supplied to a mold,a pellet is pressed, the pressing die is retracted, the pellet isejected, the ejector retracted, and a fresh charge of material suppliedto the mold. By utilizing fluid exhausted upon first of said powerunits, said valve mechanism being operative to effect the reciprocationof the first ram; fluid conducting means connecting the outer ends ofsaid power units to apply fluid exhausted from the first power unitduring retraction of the first ram to said second unit to cause theretraction of the pressing ram, for operating the article ejector theseoperations are properly synchronized without the necessity of extraneoustiming mechanism,

While only two circuits have been illustrated, it should be obvious thatmany minor modifications may be made therein without departing from thefundamental principles set forth in the following claims.

7 W e claim:

1. A mechanism for pressing articles comprising a source of fluidpressure; a power unit having a ram for cooperation with forming toolsand piston sections of different areas connected with said ram; meansfor directing fluid from said pressure source to said power unit to movesaid ram toward and away from said forming tools; means for ejecting aformed article from the forming tools, said means having a second powerunit with a ram and piston; and means connecting the first and secondpower units and operating to apply fluid exhausted by the piston sectionof the first power unit having the smaller area to the piston of thesecond power unit to effect movement of the second ram and ejection offormed articles; and, means forming a part of the smaller piston sectionof the first power unit for interrupting the application of exhaustfluid to the piston of the second power unit when said first power unitreaches a predetermined stage of operation.

2. In a hydraulic pressing apparatus, a source.

of fluid pressure; first and second power units having reciprocablerams; a control valve mechanism between said source of pressure and thefirst of said power units, said valve mechanism being operative toeffect the reciprocation of the first ram; fluid conducting meansconnecting the outer ends of said power units to direct fluid exhaustedthe projection of the second ram; means normally urging the second ramtoward a retracted position; a valved passage means operative when saidfirst ram reaches a predetermined point during retraction to establishcommunication between the opposite ends of the cylinder of said secondpower unit.

4. In a hydraulic pressing apparatus a source of fluid pressure; a powerunit having piston and cylinder sections of diiierent areas; controlvalve mechanism between said pressure source and said power unit; saidcontrol mechanism being operative to effect the reciprocation of thepiston section of said power unit, a second power unit disposed inopposed relation to the first-' mentioned power unit; fluid conductingmeans establishing communication between the outer ends of both sectionsof said first and said second power units; means normally tending tomove the piston of said second power unit to a retracted position; andvalved passage means operative when the piston section of said firstpower unit reaches a predetermined position during retractive movementto establish communi-' cation between opposite ends of the smallercylinder section of said first power unit.

5. In a hydraulic pressing apparatus, a source of fluid pressure; firstand second power units having reciprocable rams; a control valvemechanism between said source of pressure and the first of said powerunits, said valve mechanism being operative to eiiect the reciprocationof the first ram; fluid conducting means connecting the outer ends ofsaid power units to apply fluid exhausted from the first power unitduring retraction of the first ram to said second unit to cause theprojection of the second ram; means normally urging the second ramtoward a retracted position; and valved passage means operative whensaid first ram reaches a predetermined point during retraction toestablish com-- of fluid pressure; first and second power. units havingreciprooable rams; a control valve mechanism between said source ofpressure and the first of said power units, said valve mechanism beingoperative to effect the reciprocation of the first ram; fluid conductingmeans connecting the outer ends of said power units to apply fluidexhausted from the first power unit during retraction of the first ramto said second unit to cause the projection of the second ram; meansnormally urging the second ram toward a retracted position; and valvedpassage means operative when said first ram reaches a predeterminedpoint during retraction to establish communication between the oppositeends of the cylinder of said second power unit and a second meansselectively operable to establish communication between the oppositeends of the cylinder of said second power unit prior to the time thefirst ram reaches said predetermined point in its retraction movement.

7. In a hydraulic pressing apparatus, a source of fluid pressure; apower unit having piston and cylinder sections of different areas;control valve means between said pressure source and said power unit;said valve means being operative to alternately connect the inner andouter ends of the larger cylinder section of said power unit with saidpressure source to effect reciprocation of said piston sections; asecond power unit having a piston and cylinder disposed in opposedrelation to said first power unit; a fluid passage establishingcommunication between the outer ends of the smaller cylinder section ofthe first and the cylinder of said second power units; a second fluidpassage establishing communication between the outer end of the largercylinder section of the first power unit and the inner end of the secondpower unit; a check-valve containing passage connecting said first andsecond passages, said check valve limiting fluid flow to a directionfrom the second to the first passage; another valved passage operativewhen the piston sections of said first power unit reach a predeterminedposition during retraction to establish communication between the outerends of the cylinder sections of said first power unit; and meansyieldably urging the piston of said second power unit toward a retractedposition.

8. In a hydraulic pressing mechanism, a source of fluid pressure; apower unit of the piston and cylinder type; a control valve mechanismbetween the pressure source and said power unit, said valve mechanismbeing operative to alternately connect the ends of said cylinder to saidpressure source to effect reciprocation of said piston; a second powerunit of the piston and cylinder type mounted in opposed relation to thefirst power unit; a fluid conductor connecting the outer ends of thecylinders of said power units; and valve means in said conductorresponsive to fluid pressure when the outer end of the cylinder of saidfirst power unit is connected with said pressure source to interruptcommunication between the outer ends of the first and second cylindersand to connect the latter to exhaust.

9. In a hydraulic pressing mechanism, a source of fluid pressure; apower unit of the piston and cylinder type; a control valve mechanismbetween the pressure source and said power unit, said valve mechanismbeing operative to alternately connect the ends of said cylinder to saidpressure source to effect reciprocation of said piston; a second powerunit of the piston and cylinder type mounted in opposed relation to thefirst power unit; a fluid conductor connecting the outer ends of thecylinders of said power units; a flow control mechanism for regulatingthe rate of movement of the piston in said second power unit; and valvemeans in said fluid conductor operative to render the flow controlmechanism effective.

10. In a hydraulic pressing mechanism, a source of fluid pressure; apower unit of the piston and cylinder type; a control valve mechanismbetween the pressure source and said power unit, said valve mechanismbeing operative to alternately connect the ends of said cylinder to saidpressure source to effect reciprocation of said piston; a second powerunit of the piston and cylinder type mounted in opposed relation to thefirst power unit; a fluid conductor connecting the outer ends of thecylinders of said power units; and valve means in said conductorresponsive to fluid pressure when the outer end of the cylinder of saidfirst power unit is connected with said pressure source to interruptcommunication between the outer ends of the first and second cylindersand to connect the latter to exhaust; a flow control mechanism forregulating the rate of movement of the piston in said second power unit;and means operated by the piston of said first power unit at apredetermined point in the retraction thereof to render said flowcontrol mechanism eifective.

CECIL E. ADAMS. ELLIS H. BORN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,112,466 Maloon Mar. 29, 19382,192,778 Stacy Mar. 5, 1940 2,243,716 Monroe May 27, 1941 2,280,849Pocock Apr. 28, 1942 2,337,578 Schultz Dec. 28, 1943

